1. Field of the Invention
The present invention relates to an ultrasonic linear motor suitable for use as a driving source in electronic equipment and in precision instruments.
2. Description of the Prior Art
Recently, there has been developed an ultrasonic motor using a piezoelectric element formed of piezoelectric ceramics serving as a driving source for generating ultrasonic vibration, and this ultrasonic motor is utilized as an actuator for various kinds of equipment. Such an ultrasonic motor has the advantages that it is compact and generates a high torque. Furthermore, since the ultrasonic motor using a piezoelectric element does not generate an electromagnetic wave, an electromagnetic medium is not affected by the motor.
The ultrasonic motor includes a driving member vibrated by the driving source, and the driving member is located in contact with a driven member, so that the vibration of the driving member in a driving direction may be frictionally transmitted to the driven member. The driving member generates a linear vibration or an elliptical vibration as a result of a synthesis of vibrations in two directions perpendicular to each other. Such an ultrasonic motor is structurally classified as a vibrating reed type, a torsional vibrator type or a travelling wave type.
FIG. 18 shows a vibrating reed type ultrasonic motor constructed of a piezoelectric vibrator 11 vibrating in its longitudinal direction and a vibrating reed 12 attached to the piezoelectric vibrator 11. The vibrating reed 12 is located in oblique contact with a surface of a driven motor 13, so that the driven member 13 may be driven by the vibrating reed 12 in a given direction. The ultrasonic motor of this type exhibits a high energy conversion efficiency and operates at high speed.
FIG. 19 shows a torsional vibrator type ultrasonic motor constructed of a piezoelectric vibrator 14 vibrating in its longitudinal direction and a torsional connecting member 15 attached to the piezoelectric vibrator 14. The torsional connecting member 15 is flexed by the longitudinal vibration of the piezoelectric vibrator 14 to thereby generate rotational displacement about an axis of the piezoelectric vibrator 14, resulting in the generation of elliptical vibration rather than the linear vibration as mentioned above.
FIG. 20 shows a travelling wave type ultrasonic motor constructed of an annular or disk-like vibrating member 16 and a piezoelectric element 17 attached to the vibrating member 16. The vibrating member 16 is provided with a flexural wave travelling in a circumferential direction by the piezoelectric element 17. A rotor 18 is disposed in contact with the vibrating member 16, so that a contact surface of the rotor 18 contacting the vibrating member 16 is elliptically vibrated by the flexural travelling wave. The ultrasonic motor of this type has the advantage that the contact surface is less subject to wear because the surface area thereof is large.
However, the above-mentioned prior art ultrasonic motors have the following deficiencies.
In the vibrating reed type ultrasonic motor as shown in FIG. 18, the vibrating reed 12 is vibrated by the piezoelectric vibrator 11 to intermittently contact the driven member 13. As a result, the operation of the drive member 13 is unstable, and the driving direction cannot be changed. Further, the tip of the vibrating reed 12 tends to wear out.
In the case of using the torsional vibrator type ultrasonic motor as a linear motor, it is necessary to provide a linear motion converting mechanism.
Similarly, in the case of using the travelling wave type ultrasonic motor as a linear motor, it is necessary to provide a linear motor converting mechanism. Further, the travelling wave type ultrasonic motor has the disadvantage that the energy conversion efficiency is low. If the annular or disk-like vibrating member 16 is replaced by a linear vibrating member to transmit the travelling wave vibration of the linear vibrating member to a linear driven member such as a rail, the travelling wave vibration is transmitted to the rail, causing an increase in energy loss and thus reducing efficiency.